Video: Welcome to MSNBC, Rachel!

NEW YORK — MSNBC talk show host Keith Olbermann is getting a new running mate, Rachel Maddow, who will follow Olbermann’s “Countdown” with her own prime-time hour starting next month.

Maddow, a political commentator who is heard daily on the Air America Radio network and has served as a guest host for Olbermann, will launch her MSNBC show Sept. 8, the network announced Wednesday. (Msnbc.com is a joint venture between NBC Universal and Microsoft).

“The Rachel Maddow Show,” billed as “a smart look at politics, pop culture and all the day’s top stories,” will originate weeknights at 9 p.m. EDT.

Before claiming the time slot currently occupied by Dan Abrams, she will be a political panelist during MSNBC’s coverage of the Democratic and Republican national conventions.

Abrams, one-time MSNBC general manager, stepped in with his nightly political and legal affairs hour, “Verdict,” when Joe Scarborough moved to mornings last year. Abrams will remain chief legal correspondent for NBC and MSNBC, and contribute to “Dateline NBC” and “Today,” among other duties. The final edition of “Verdict” airs Thursday.

Like its rival all-news cable networks, MSNBC has pumped up its political coverage during the presidential race. Though retaining a third-place standing overall against perennial ratings champ Fox News Channel and runner-up CNN, it has shown significant audience growth, especially among younger viewers.

Olbermann’s program has particularly proved a breakout success. With his liberal slant and sharply anti-Bush-administration stance, Olbermann has emerged in the eyes of many viewers as the left-wing response to Fox, which is dominated by conservative hosts including Bill O’Reilly and Sean Hannity.

Maddow seems to represent a comfortable ideological fit with Olbermann, whose show airs at 8 p.m. EDT. Since being named an MSNBC political analyst last January, Maddow has subbed for Olbermann and has frequently contributed to his show.

She will also continue her radio show on Air America, a liberal-focused network where she has been heard since it signed on in 2004.